The snap visit this week of veteran U.S. diplomat Richard Holbrooke to Georgia - ostensibly to discuss Georgian participation as a supply route to the Afghanistan battlefront - underscores an unsettling new development in U.S.-Russian relations. At the ragged edge of the old East-West divide, a new battle is taking shape: this one for influence over - and under - the Black Sea.

For much of the Cold War, the Black Sea was bounded by territory under Soviet control - the Georgian, Ukrainian and Russian Soviet Socialist Republics on the eastern shore, Warsaw Pact members Romania and Bulgaria on the west - with Turkey providing NATO its sole, albeit geo-critical position at the throat of the Black Sea.

With Romania and Bulgaria's accession to NATO in 2004 alongside the Color Revolutions in Georgia and Ukraine, the prospect opened in 2004-5 of a future in which all Black Sea nations save Russia would be NATO nations. The concept of the Black Sea as a "Russian Lake" - a status that spanned the reign of Catherine the Great to the waning days of the Cold War - seemed destined for the dustbin of history.

Today, history may be doubling back, with the Georgia war demonstrating Russia's willingness to use force to advance its aims, and Ukraine's election of a pro-Russian president signaling Kiev's shift from Orange to Red in its political orientation.

Developments on the western shore of the Black Sea have been equally dramatic. Early this month - just when Moscow was likely hoping that the September 2009 scuttling of the Bush Era Ballistic Missile Defense (BMD) plan in Poland and the Czech Republic was a sign of American decoupling from Eastern Europe - the U.S. made a surprise announcement welcoming Romania's participation in the Obama administration's revamped BMD system.

The U.S.-Romania announcement was followed immediately by rumors of additional BMD components in Bulgaria and Turkey, a land-based presence that, in addition to being well-sited to defeat an Iranian missile threat, would lock in U.S. regional involvement for the indefinite future. Indeed, and in sharp contrast to the Bush plan, the Black Sea itself may prove critical to the Obama BMD scheme: A 2009 report by the U.S. Congressional Research Service notes that U.S. Navy BMD destroyers and cruisers armed with SM-3 interceptors might require deployments not only in the eastern Mediterranean but in the Black Sea as well. The prospect is more than theoretical: This past summer, the USS Stout, a BMD destroyer, paid port of call visits to Constanta, Romania, Varna, Bulgaria and the Georgian ports of Batumi and Poti.

Not to be outdone, the Russian Navy has now struck a deal to buy France's Mistral amphibious landing vessel (France's NATO membership notwithstanding), which, in the words of one overly candid Russian admiral, would have enabled Russia to wrap up the Georgia war "in 45 minutes." Days later, Russian media carried a report out of the pro-Russian break-away enclave of Transdniestr - a sliver of Moldova, just now engaged in a new round of unity flirtations with Romania - professing that it would be pleased to host Russian Iskander missiles to counter the looming U.S. BMD threat. No word yet on whether Moscow marionettes South Ossetia or Abkhazia will follow suit.

As if all this missile-flexing weren't enough, there's an economic dimension to the Black Sea conflict. The Black Sea figures in Russia's South Stream pipeline scheme to transit Russian-sourced natural gas as far west as Austria and Italy - itself a means of undercutting the much-discussed, much-delayed Nabucco pipeline billed as a western-backed way of reducing Russian resource dominance. Add to that the 2009 ruling by the International Court of Justice in the Black Sea boundary dispute recognizing Romania's sovereignty over a swath of the Black Sea bed (Ukraine, much more pliable to Russian pressure, was the loser) which puts the undersea exploitation of sizable oil and gas fields in the hands of a NATO nation. For resource-rich Russia, Romania's gain is unwelcome competition - not so much in lost energy revenues, but in a diminished Russian capability to use its energy weapon against Europe. Expect a rear-guard Russian game of resource-denial aimed at European and North American companies that might provide an alternative energy supply to Central Europe and beyond.

With so many other challenges to reckon with, is the U.S. really ready for a post-Cold War tug of war in Southeastern Europe? Conventional wisdom posits that President Obama - who cancelled plans to attend the Madrid EU summit this May and has his own plateful of domestic and international crises to attend to - has little mind-space to devote to such machinations. But this presidential-level "delegation" leaves the United States' European policy largely in the hands of two Obama cabinet members - Republican holdover Defense Secretary Robert Gates and Secretary of State Hillary Clinton - who together form a line of continuity from Bush I through the Clinton years and Bush II, a period in which U.S. policy demonstrated a reasonably bipartisan appreciation of the value of a Europe whole and free. And as the Holbrooke photo-op in Georgia (never mind how Tbilisi would run a supply line from the wrong side of the Caspian Sea to surging NATO forces in Afghanistan) and BMD basing agreements make clear, this sub-presidential policy approach shows few signs of giving Russia the regional free hand it seeks.

Pipelines criss-crossing the seabed, extraction platforms dotting the coastlines, U.S. missile defense cruisers and destroyers patrolling the surface and paying visits to ports of call, while the Russian Navy anchors at its Ukrainian rent-a-port at Sevastopol: As the decade unfolds, the Black Sea is about to become a busy place. All of which will offer plenty of opportunities for contending forces and clashing interests - military as well as economic - to come into contact.

65 years ago this month, at the Black Sea resort of Yalta, the world's powers mapped the ending of one war while planting the seeds of another. Today, the Black Sea once again figures as a potential fault line for a new round of friction between East and West.

Daniel McGroarty, principal of Carmot Strategic Group, an issues management firm in Washington, D.C., served in senior positions in the White House and at the Department of Defense.